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Serotonin syndrome — USMLE Step 3 MCQ

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HardPsychiatry (outpatient management)Serotonin syndromeUSMLE Step 3

A patient taking valproate develops vomiting, lethargy and confusion. Ammonia is 146 µmol/L, but AST, ALT and bilirubin are normal. What is the best medication step?

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Correct answer: A — Stop valproate and treat the hyperammonemic encephalopathy

The best answer is “Stop valproate and treat the hyperammonemic encephalopathy”. Valproate-associated hyperammonemic encephalopathy can occur despite normal liver tests. New compatible symptoms require ammonia assessment and discontinuation of valproate, with supportive and targeted management based on severity. Unexplained lethargy, vomiting or mental-status change during valproate therapy warrants ammonia measurement; hyperammonemic encephalopathy can occur with normal liver tests and requires discontinuation.

Reference: FDA Prescribing Information: VALPROIC ACID: https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=4067a52d-c3fa-4531-8e4f-9675e494065f&type=display